Individual bypass injector valves for a double bypass variable cycle turbofan engine

Abstract

A double bypass, variable cycle gas turbofan engine is provided with a variable area bypass injector which varies the area through which the inner bypass stream is injected into the outer bypass stream. The bypass injector comprises an upstream variable area, double bypass selector valve, the position of which determines whether the engine will operate in the single or double bypass mode, and a downstream static pressure valve which defines an optimum flow path for injecting the inner bypass stream into the outer bypass stream. The ability to vary the area through which the inner bypass stream is injected into the outer bypass stream permits the static pressure valve to operate as an ejector and permits control of the two bypass air streams through creation of a static pressure balance at the exit of the variable area bypass injector. The ability to control the bypass operating mode and the static pressure balance at the confluence of the two bypass streams eliminates the necessity for one exhaust duct and one exhaust nozzle, thereby reducing complexity and weight, and improves the engine-aircraft integration by reducing engine and nozzle diameters.

Having thus described the invention, what is claimed as novel and desired to be secured by Letters Patent of the United States is: 
     
       1. A method for modulating the bypass flows of a gas turbofan engine having a core engine, a front fan section for pressurizing air, an outer bypass duct for bypassing a stream of pressurized air around the core engine, an aft fan section for further pressurizing air discharged from the front fan section, an inner bypass duct for bypassing an airstream from the aft fan section around the core engine, and a common bypass duct for receiving confluent flow from the inner and outer bypass ducts and bypassing the confluent flow around the core engine, comprising the step of: varying the area through which the inner bypass airstream is injected into the common bypass duct to match the static pressure of the inner bypass stream to the static pressure of the outer bypass stream prior to mixing the two streams at their point of confluence.   
     
     
       2. The method as recited in claim 1 further comprising the steps of accelerating the inner bypass airstream to reduce the static pressure within the outer bypass duct to a value less than that of the air exiting the front fan section, and opening the outer bypass duct to receive a portion of the pressurized air from the front fan section, and thereafter varying the area through which the inner bypass airstream is injected into the common bypass duct to match the static pressure of the outer bypass stream prior to mixing the two streams at their point of confluence. 
     
     
       3. The method as recited in claim 1 further comprising the steps of closing the outer bypass duct to the flow of air from the front fan section, further pressurizing all of the air from the front fan section through the aft fan section, and expanding the inner bypass stream into the common bypass duct. 
     
     
       4. The method as recited in claim 3 further comprising the steps of thereafter mixing the common bypass duct stream with fuel and combusting the resulting mixture. 
     
     
       5. An improved gas turbofan engine of the type having a core engine, a front fan section for pressurizing a flow of air, an outer bypass duct for bypassing a stream of pressurized air around the core engine, an aft fan section for further pressurizing the air discharged from the front fan section and an inner bypass duct for bypassing an airstream from the aft fan section into the outer bypass duct and around the core engine, wherein the improvement comprises: a common bypass duct for receiving confluent streams from the inner and outer bypass ducts and bypassing the confluent flow around the core engine; and   a variable area bypass injector for selectively modulating and separating the airstreams through the inner and outer bypass ducts including static pressure valve means for varying the area through which the inner bypass duct airstream is injected into the common bypass duct at the point of confluence of the inner and outer bypass ducts, and a bypass selector valve associated with the outer bypass duct and which is operable between two positions, one at which flow through the outer bypass duct is prohibited and another at which flow through the outer bypass duct is permitted.   
     
     
       6. The improved gas turbofan engine as recited in claim 5 wherein said static pressure valve means comprises a translating section of an intermediate casing disposed between and partially defining said inner and outer bypass ducts at their point of confluence and means for positioning said translating section, and wherein said translating section cooperates with an inner casing housing said core engine to define a variable area orifice for the passage of the inner bypass stream therebetween. 
     
     
       7. The improved gas turbofan engine as recited in claim 5 wherein said bypass selector valve comprises a translating valve positionable between a first position where it seals the end of the outer bypass duct proximate the front fan section and a second position where it is retracted into an outer casing partially defining the outer bypass duct, and means for translating said valve between the two positions. 
     
     
       8. A gas turbofan engine of the type having a front fan section for pressurizing a flow of air, generally coannular inner and outer bypass ducts for receiving the flow of air as airstreams and, a variable area bypass injector for selectively modulating the pressurized airstreams passing through the generally coannular inner and outer bypass ducts and for selectively mixing the airstreams in a common bypass duct wherein the variable area bypass injector comprises: a two-position bypass selector valve associated with the outer bypass duct, said valve having a first position essentially parallel to the pressurized airflow wherein flow through the outer bypass duct is prevented and a second position wherein an airstream is permitted to flow through the outer bypass duct; and   static pressure valve means for varying the area through which the inner bypass duct airstream is injected into the common bypass duct at the point of confluence of the inner and outer bypass ducts.